1. Field of the Invention
The invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for forming a titanium or titanium compound film by the CVD method in such semiconductor devices as bipolar LSI, MOS LSI or the like, provided with a contact plug for a multi-layer wiring.
2. Description of the Related Art
Techniques for multi-layer wiring in semiconductor devices provide such advantages that discrete devices can be laid out on a chip without separate consideration of wiring spaces on the chip, thereby enabling devices to be increased in the scale of integration and further microminiaturized. In this regard, there must be good contact between a contact plug and silicon substrate.
The contact plug has hitherto been made of conductive materials, such as W, poly-Si, Al-Si or the like, and a multi-layer wiring of W, Al-Si or the like.
When devices are further microminiaturized, aspect ratios of contact hole inevitably becomes higher and contact resistance increases, resulting in such a defect that the required contact property is unobtainable. Also, the contact plug made of the above conductive materials is extremely sensitive to a natural oxide film on the interface between the contact plug and the silicon substrate and deteriorates the contact property. Particularly when made of tungsten the plug sometimes the erodes silicon substrate to deteriorate the contact property correspondingly to a higher aspect ratio.
Also, the multi-layer wiring has various problems in efficiency and reliability due to the quality of the material used as the width of the wiring is made smaller.
Hence, it is desired to solve the above various problems related to the contact plug and the multi-layer wiring to facilitate development of new devices for the next generation.
Under these circumstances, research has focused on a method for coating a titanium film with good coverage using a CVD method. For coating a titanium film the substrate needs to be heated. In this process, heating the substrate to a decomposition temperature (about 800.degree. C. or more) of e.g., titanium tetrachloride, results in an excessively elevated temperature in the substrate, thereby causing an undesired reaction between Ti and Si. Besides, an aluminum alloy as used for wiring may be affected at such high temperature. Employing plasma energy in place of thermal energy deteriorates the coverage in CVD method. In addition, using titanium tetrachloride as material gas results in a titanium film containing chlorine (Cl). In other words, using titanium tetrachloride has a drawback of allowing wirings to be corroded (due to the difficulty of impeding the infiltration of chlorine content in the titanium film when using aluminum alloy as wirings in the subsequent process).
Thus, only with difficulty does the CVD method using titanium tetrachloride provide a titanium film with only a small amount of impurities and with good coverage at low temperature.